TRANSACTIONS OF SECTION I. 887 
tissues which are inhibited have a great tendency to contract of themselyes—that 
is, they form certain very unstable substances. In closely related tissues which are 
not inhibited this tendency exists but little or not at all. The proximate cause 
of inhibition might then be that the nervous stimulus causes certain molecules of 
the tissue to form more stable combinations. This need not be associated with any 
general assimilation ; it would simply make the muscle adopt for a time a mode of 
life more like that of other closely related muscle. 
Number of Relay Stations—I have already mentioned that the nerve-fibres 
which pass from the central nervous system to the involuntary tissues do not run 
to it direct, but end in groups of nerve-cells or ganglia from which fresh nerve- 
fibres are given off. Now, in most cases, there are anatomically several ganglia on 
a nerve in its course from the spinal cord to the periphery. For example, the 
nerve-fibres which cause the hairs of a cat’s tail to stand on end, giving the tail the 
appearance of a bottle brush, leave the spinal cord in the lower part of the back, 
and enter a nerye-strand which is beaded with ganglia. They leave this strand 
near the root of the tail. Between the point where the nerve-tibres enter and the 
point where they leave the strand there are seven or eight ganglia. The fact 
offers us a problem of some difficulty. With how many of these ganglia are the 
nerve-fibres connected ? Or, in other words, how many relay stations are there ; 
eight or one, or some intermediate number? Further, do all kinds of involuntary 
Fia. 1. 
nerve-fibres in all parts of the body have the same number of relay stations, or do 
some have one, some two, some three, and so on? It would take too long to 
discuss this question here. But the experimental evidence is, I think, fairly 
decisive in favour of the simple view that the nerve-impulse passes through one 
relay station only. There is, however, evidence that the nerve-fibres which pass 
from the spinal cord branch, so that we may take the element by reduplication of 
sig — involuntary nervous system is built up to be diagrammatically as 
in fig. 1. 
Reflewes,—Another point of view is given by a comparison of the groups of 
nerve-cells of the peripheral ganglia with the groups of nerve-cells of the brain 
and spinal cord. The proper working of the body depends upon an agile response 
by the central nervous system to what is going on in the periphery. Now the 
peripheral ganglia are made up of nerve-cells and nerve-fibres which differ less in 
general characters from some of the cells of the central nervous system than these 
differ from one another. The nerve-cells of the spinal cord can receive impulses 
from many groups of nerve-cells both near and remote; they do not simply receive 
impulses from one quarter alone—say, the cortex of the cerebral hemispheres— 
but from many quarters, and notably direct from the periphery. Hence it has 
been supposed that the peripheral ganglia have similar wide connections, that they 
